Liquid fuel gas dynamic mixing laser

ABSTRACT

A liquid fuel is admitted to a catalytic chemical reactor and decomposed to provide high temperature, vibrationally excited nitrogen. The nitrogen is aerodynamically expanded to a condition of low static temperature and carbon dioxide is then admixed. Vibrational energy is transferred from the nitrogen to the carbon dioxide causing a population inversion in the carbon dioxide which emits laser energy in an optical cavity.

[451 Sept. 26, 1972 United States Patent Burwelletal.

[54] LIQUID FUEL GAS DYNAMIC MIXING LASER [72] Inventors: Wayne G.Burwell, Wethersfield;

Charles Oickle, Jr., New Britain, both of Conn.

Assignee: United Aircraft Corporation, East Sayer, InternationalAerospace Abstracts, Vol. 10, No. 16, Aug. 15, 1970, No. A70- 33603, p.2,856.

Hartford, Conn.

Dec. 18, 1970 Primary Examiner-Ronald L. Wibert Assistant Examiner-R. J.Webster [22] Filed:

Appl. No.: 99,439

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3,165,382 1/1965 Forte...........................23/2l2 3,571,747 3/1971Bronfin et a1.............331/94.5 10 Claims, 3 Drawing FiguresPATENTEDsms I972 SHEET 3 UF 3 LIQUID FUEL GAS DYNAMIC MIXING LASERBACKGROUND OF THE INVENTION devices in the past several years hasresulted in sophistilo cation of various laser apparatus currently underdevelopment. The gas dynamic laser which has grown out of the initiallaser effort, is representative of one of the more sophisticated lasertechniques and has the potential of providing very high power radiationoutput, due primarily to the large gas handling capabilitycharacteristic of such a system and to the large quantity of energywhich can be added to the gases flowing in such systems.

Gas laser operation requires that a population inversion be establishedbetween upper energy levels and lower energy levels of the lasingmedium. In a simplified functional description of the carbondioxidenitrogen laser, carbon dioxide molecules are excited from theground vibrational energy level (000) to an upper vibrational energylevel (001) the upper lasing level by collision with vibrationally (V=l)excited nitrogen and then stimulated to emit electromagnetic radiation.The emission causes the carbon dioxide to assume an intermediatevibrational energy level (100) the lower lasing level for a period oftime before returning to the ground (000) level, passing through anon-laser emitting (010) level in the process. Successfully maintainingthe population inversion necessary to laser output requires controllingthe rates at which the carbon dioxide molecules pass through all thevarious energy levels, and unless the 0l0level can receive all thel000l0 transitions, the number of carbon dioxide molecules producinglaser energy (undergoing the 001-100 transition) is reduced.

The non-emitting 010 level which exists between the lower lasing 100)level and the ground level has a relatively long natural relaxation timeand presents a natural bottleneck in the overall carbon dioxide energyexchange process. However, certain relaxant gases such as water vapor,helium or hydrogen readily couple with carbon dioxide at the 010 levelproducing an alternate energy release mechanism sufficient to avoid thedescribed bottlenecking in the energy exchange processes.

The 001 energy level of a carbon dioxide molecule is preferentiallypumped by collision with vibrationally excited nitrogen, due to anaturally occuring match of energy levels between these two gases. inaddition to the matched energy level characteristic, nitrogen has arelatively long lifetime in the first vibrational (V=l) level (comparedto a short lifetime of the carbon dioxide at the corresponding 001level), and when vibrationally excited nitrogen is mixed with carbondioxide, the nitrogen preferentially transfers its vibrational energy tocarbon dioxide molecules upon collision therewith, the nitrogenreverting to the ground (V=0) state and the carbon dioxide assuming anexcited or lasable state having a relatively short lifetime.

The gas dynamic laser terminology refers to an excitation or pumpingtechnique whereby tee laser pumping gas such as nitrogen isvibrationally excited. In some of the more desirable working systems, anitrogen gas is heated from a thermal source, allowing the molecules toassume an equilibrium distribution appropriate for the elevatedtemperature, and distribution containing a small amount of vibrationallyexcited nitrogen. The gas molecules are then rearranged in anonequilibrium distribution by dynamic means by passing them through anaerodynamic expansion nozzle whereby some of the molecules aretransferred to the ground vibrational level and some other moleculesremain in the first vibrational level due to their relatively longnatural relaxation time. The nitrogen which is at supersonic velocity inthe nozzle is immediately mixed with carbon dioxide thereby ensuringthat the vibrationally excited nitrogen does not revert to the groundstate before colliding with and transferring this vibrational energy tothe carbon dioxide. The carbon dioxide, in turn, has sufficient velocityto reach the optical cavity while still vibrationally excited. Theability to provide vibrationally excited nitrogen in a gas dynamicmanner makes possible large population inversions and in turn the lasingof carbon dioxide.

The gas dynamic laser is a relatively inefficient device, having athermal energy to laser energy overall conversion efficiency ofapproximately three fourths of 1 percent; however, if the temperature ofthe thermally excited gases can be raised sufficiently, the overallconversion efficiency can be increased by a factor of up toapproximately 4. Conversion efficiencies much higher than this areunlikely in a simple system because of the inherent characteristic ofthe various energy transfer processes involved in the production oflaser energy with a hot gas in the gas dynamic process. In a typicalcurrent system, the extraction efficiency of an optical cavity isapproximately 50 percent, the quantum efficiency for the transition ofcarbon dioxide gas from the 001 level to the level is 41 percent and thetemperatures of combustion raise about 3 percent of the population ofthe exciting nitrogen gas to the first vibrational V=l level, resultingin an overall thermalto-laser energy conversion efficiency no higherthan about three fourths of 1 percent.

Mixtures of carbon dioxide and nitrogen are desirable for the systemdescribed due primarily to the physical characteristics of these gases.For a laser application, carbon dioxide is generally provided by thecombustion of a limited number of sources, preferably carbon monoxide orcyanogen, and subsequent admixing of nitrogen is required to provide thecorrect gas mixture prior to expansion through the nozzle. Laser beamsof substantial power at a wavelength of approximately 10.6 microns havebeen produced with the type gas dynamic laser described, however, thegas-handling equipment required is large and a troublesome disadvantage.Gas dynamic lasers inherently consume a large amount of gas andtherefore require a substantial array of high pressure gas bottles,gages and associated equipment to produce a laser beam for any sustainedduration. A solution to the current problem of bulkiness would appear tobe the combustion in air of a carbon containing liquid fuel.Theoretically, the only consumable required in such a system would bethe liquid fuel, the air being freely available at the operation site;the carbon in the fuel could provide the necessary car-.

bon dioxide by combustion with the oxygen component of air, and thenecessary nitrogen would be unavoidably present due to its naturaloccurrence as the predominant component of air. However, the combustionof any fuel with air introduces a number of undesired by-products inamounts sufficient to compete with the gas molecule energy transferrequired to produce a lasing of the gas mixture. Interference offered bythese contaminants reduces the conversion efficiency of available energyto laser energy. In addition, the nitrogen-carbon dioxide molecule ratiois not optimum further reducing the overall performance of such asystem; even if a preferred fuel such as carbon monoxide or cyanogen isburned with air, the amount of nitrogen present in the combustionproducts if below optimum, resulting in a substantial reduction in theamount of lasing energy extractible from such a system.

In order to circumvent the suggested inefficient systems, carbonmonoxide and cyanogen gaseous fuels have been combusted with pure oxygento provide a highly energized source of carbon dioxide or carbondioxide-nitrogen mixture, and subsequently a controlled quantity ofnitrogen is admixed such that the total gas expanded in the gas dynamiclaser nozzle is one of the proper proportions to produce the maximumpower laser output beam. However, an optimize high output power lasersystem requires a nitrogen-to-carbon dioxide molecule ratio ofapproximately 6 to l and it is apparent that a system, particularly acarbon monoxide fuel system, relying on the combustion of a fuel inoxygen, requires that an enormous amount of bottled nitrogen accompanythe system and be available during operation. Further, the combustiblestypically are exhausted to atmosphere after lasing and a new charge ofgases is required if subsequent lasing action is desired.

SUMMARY OF THE INVENTION A principal object of this invention is theproduction of high power laser energy utilizing nitrogen gas produced bythe catalytic decomposition of a liquid fuel.

According to the present invention, a mixture of high temperaturenitrogen and other gases is produced by the decomposition of a liquidhydronitrogen fuel in a catalytic reactor, the gases being expanded in asupersonic nozzle and admixed with cooler carbon dioxide to provide apopulation inversion of vibrational energy levels in the carbon dioxidecapable of being stimulated to emit laser radiation.

The present invention eliminates the voluminous storage and handlingequipment required for the gaseous fuel and energizing gas in a gasdynamic laser; the necessity of storing toxic and difiicult to handlefeed gases is avoided also. An additional advantage of this invention isthat the energy required to raise the temperature of the nitrogen isinherently provided by the catalytic decomposition process of the liquidfuel providing the nitrogen gas. The decomposition of a hydronitrogencompound produces molecular hydrogen, as well as the nitrogen gas,providing still other advantages; these gases can be chemically reactedwith a reactant, releasing heat and raising the temperature of thenitrogen above the temperature of decomposition. Further, the reactionproducts can provide an energy exchange mechanism beneficial to thelasing of carbon dioxide.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a simplified, sectioned, planview of one embodiment of a gas dynamic mixing laser having a catalyticreactor in accordance with the present invention;

FIG. 2 is a graph illustrating the effect of catalytic reactor length onthe temperature of the decomposed products;

FIG. 3 is a graph illustrating the effect of catalytic reactor length onthe mole fraction of decomposition products.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a liquidhydronitrogen fuel source 12 communicates by suitable means, such as theconnecting pipes 14 and 16 with a chemical catalytic reactor 18 filledwith a packed bed 20 comprised of porous alumina substrate which hasbeen impregnated with noble metal. A two dimensional aerodynamic nozzle22 is attached directly to the reactor 18 in communication with a source24 of carbon dioxide by suitable means such as pipes 26 and 28. Thecarbon dioxide may be stored as a high pressure gas in which case thereis no need for pump 30. The carbon dioxide is admitted to the nozzlethrough a slot 32 located in the nozzle wall 34 at a location along thenozzle wall where full expansion of the gases passing therethrough hasnot yet occurred. An optical cavity 36 is attached to the low pressureside of the nozzle 22 as used herein optical cavity is defined as meansfor providing amplification of electromagnetic radiation by stimulatedemission of radiation from a medium having a suitable populationinversion of energy levels.

In the operation of the present invention, the liquid fuel hydrazine isremoved from the fuel source 12 through the pipe 14 by pump 38 andtransported through the pipe 16 to the chemical reactor 18. In steadystate operation, the hydrazine interacts with the catalytic packed bed20 thereby releasing heat while forming nitrogen, hydrogen and ammoniagases. These hot gases are lowered in pressure and temperature by anexpansion across the nozzle 22, and carbon dioxide from the source 24 isadmixed with the nitrogen and hydrogen in the nozzle, the carbon dioxideentering the nozzle 22 through slot 32. The gas admixture passes throughthe optical cavity 36 and discharges as exhaust gas 40, laser energyhaving been released by the admixture in the optical cavity and removedtherefrom through the laser coupling device 42 as laser beam 44. Areactants source 46 communicates by suitable means such as a connectingpipe 48 with a reaction chamber 50 which is located between the packedbed 20 and the aerodynamic nozzle 22. A porous grid 52 separates thepacked bed from the reaction chamber.

l-Iydrazine is a preferred fuel, although other hydronitrogen compoundsare suitable. A group of fuels comprising hydrogen azide (N l-l),hydrazine azide (N I-I and ammonium azide (NJ-I is suitable for use inthis invention since they provide large amounts of nitrogen at evenhigher temperature than does hydrazine. An additional group of fuelscomprising diimide (N H- triazine (N H diiminohydrazine (NJ-lbisdiazoamine (Nd-l hexazodiazene (NJ-l heptazodiazene (NJ-I andoctazotriene (N H is also suitable for use with this invention sinceeach fuel in this group provides a larger proportion of nitrogen athigher temperature than does hydrazine.

A reduction of one hundred degrees Rankine in the temperature of thenitrogen gas leaving the reactor has been found to produce a one halfpercent reduction in the number of vibrationally excited nitrogen gasmolecules. Under the best catalytic conditions, the products ofhydrazine are formed as a gas at a peak temperature of about 2,l R. Thistemperature is ample to ensure a laser device of acceptable outputpower, however, if the temperature were to be reduced significantly, thepracticality of the system would be questionable; the temperaturecondition below which this system will produce essentially no usefulpower is about 1,200 R. lfthe catalytic reactor is forced, that is, thereactor length is increased to ensure complete conversion of the inputfuel to the end products theoretically attainable, the temperature ofthe gases would be lower than the peak temperature, perhaps as much as300 R lower.

There are distinct advantages to the operation of a gas dynamic mixinglaser as contrasted with a gas dynamic laser. For example, in theformer, the gas expanded is largely nitrogen having a relatively longrelaxation time for the vibrationally excited (V=l) level, and thepopulation inversion established during expansion can therefore bemaintained over relatively long linear distances downstream of thenozzle for a given gas velocity. In the gas dynamic laser, however, thegas expanded is a mixture of nitrogen and carbon dioxide, the latterhaving a relatively short relaxation time for the vibrationally excited(V=l) level and therefore requiring that the optical cavity bephysically near the expansion nozzle. Unless the transit time for theexpanded gases from the nozzle to the optical cavity is less than thedecay time for the 100 level carbon dioxide, the population inversion islost before the gas enters the optical cavity and the depleted gas doesnot lase. Also, in the mixing configuration the carbon dioxide isinjected at a relatively cold temperature, resulting in only a minimalpopulation of the carbon dioxide lower energy levels before lasingactivity is initiated. Mixing the carbon dioxide at a temperature ofapproximately 550 R avoids having the lower vibrational levels of thecarbon dioxide occupied due to the thermal activity of the gas. Perhapsmore importantly, the mixing laser inherently is a higher efficiencydevice; in a non-mixing system, all the gases are premixed prior toexpansion and the pumping gas, typically nitrogen, is subjected toenergy loss mechanisms by collision with the other gases present. Thesecollisions result in a decrease in overall conversion efficiency sinceenergy which would otherwise be available for lasing is transferred fromthe nitrogen by the collision processes before expansion occurs. Thereis an optimum temperature above which the amount of energy which isbeing lost by the collision processes is greater than the amount ofadditional vibrational energy which is being transferred to the nitrogenpumping gas. In a mixing system, however, the pumping gas is heatedwhile still segregated from the remaining gases and theoretically thehigher the temperature of the pumping gas prior to expansion, the higherthe potential conversion efiiciency of the system.

In the present invention with hydrazine fuel, ammonia and hydrogenproduct gases are present during the nitrogen expansion, however, theydo not interact with the nitrogen in exactly the same manner as doescarbon dioxide. Actually, these product gases can provide certainadvantages to the mixing laser concept. For example, they can be reactedin the chamber 50 with a reagent such as hydrogen peroxide, chlorinetrifluoride or chlorine pentafluoride, thereby decreasing the amount ofproduct gas and increasing the temperature of the nitrogen stream. Also,some of the reactions produce water molecules which promote relaxationof the 010 (bottleneck) level of carbon dioxide. The presence of somewater in the lasing gas mixture is advantageous, however, too much wateris undesirable. There is no sharp upper limit on the tolerable amount ofwater, but if the lasing gases comprise more than about 10 percent byvolume of water vapor,the system power output decreases appreciably. Onthe other hand, ammonia in particular, accepts vibrational energy fromthe carbon dioxide and can put a constraint on the overall systemdesign. The presence of ammonia in amounts of up to about one percent ofthe total gas, flow through the nozzle is acceptable; in higherproportions, the ammonia begins to significantly reduce the output powerfrom the lasing cavity. In this invention, the amount of ammonia in thegas can exceed one percent, however, the energy loss mechanism describedis avoided in much the same manner as the gas dynamic laser systemavoids loss of the vibrational energy in the carbon dioxide molecules.The optical cavity is placed at a short distance from the nozzle exitsuch that the ammonia does not deplete a substantial amount of theexcited carbon dioxide molecules before said molecules have entered thecavity region. The azide fuels produce relatively less ammonia atelevated temperature than hydrazine fuel and they are desirable in thisrespect.

The design of the chemical reactor wherein the catalytic decompositionof the hydrazine takes place represents an engineering compromise. Thebreak down of hydrazine theoretically produces pure hydrogen andnitrogen; as a practical matter, ammonia is also formed since thereaction does not go to completion, and the amount of ammonia so formedcan be substantial if the catalytic reactor is overly short. Theindependent variable in the reactor design is the length of thecatalytic bed through which the hydrazine fuel is allowed to pass in theprocess of decomposing into its constituent elements; dependentvariables are the temperature of the gases produced and the molefraction of the gases hydrogen, nitrogen, ammonia, and hydrazine.

A curve of the temperature of the decomposed gases as a function of thecatalytic reactor length is shown in FIG. 2. From these data,temperature considerations indicate that a relatively short reactorapproximately three tenths of an inch in length would be preferred sincean effluent gas having a temperature of approximately 2,150 R would beprovided. However, from FIG. 3 it is apparent that a reactor of thislength would produce an effluent gas mixture having an undesirably highammonia mole fraction. The data of FIG. 3 indicates further that as thereactor length is increased,

the ammonia content in the gases is decreased. Therefore, from a gascomposition point of view, a reactor much longer than three tenths of aninch is desired. As a practical matter, the reactor length isestablished by selecting a maximum temperature which does not allow thereactor to yield an unacceptably high mole fraction of ammonia.

An additional consideration in the reactor design, is the pressure dropintroduced by the catalytic bed in the flowing hydrazine stream. Thelonger the bed becomes for a given set of conditions, the greater is thepump work required to overcome this pressure drop. The porous bed,comprised of a commercial catalyst obtained under the name of Shell 405,has been found to perform satisfactorily in the reactor. This catalystcomes in a variety of sizes and shapes; cylindrical pellets one eighthinch in both diameter and length have been found to be a practicalselection. When the catalyst size becomes smaller than one eighth inch,the fuel is decomposed very efficiently but there is a relatively largepressure drop across the packed bed of the reactor; alternatively,larger size pellets tend to result in inefficient use of the fuel and alow pressure drop. The composition and method of manufacturing the Shell405 catalyst is proprietary, however, the material is substantially aporous alumina substrate covered by metal which is essentially iridium.Any of the noble metals should function as an effective catalyst.

The nozzle design required in the operation of this invention must meeta few simple criteria. It has been found, for example, that the lengthof the nozzle must be such that, having considered the velocity of thegases being expanded through the nozzle, the relaxation time of thevibrational mode for the gas must be greater than the residence time ofthe gas in the nozzle. Failure to satisfy this criterion allows the gasto relax before exiting the nozzle and since the relaxed or deexcitedgas is unable to selectively pump the lasing gas, no lasing actionoccurs. This subject is discussed more fully in Anderson, John D. Jr.,Time-Dependent Analysis of Population inversions in an Expanding Gas,The Physics of Fluids, Vol. 13, No. 8, August 1970, p. 1,983.

It has been found also that if the nozzle expansion surfaces are notcontinued (in the direction of the gas flow) beyond the point at whichthe carbon dioxide lasing gas is injected, admixing carbon dioxide tothe flowing gas stream causes the stream temperature to rise; withoutexpansion after injection, some of the carbon dioxide becomes thermallyexcited into the 010 level, an undesirable condition for lasing of thecarbon dioxide gas.

A third limitation upon the nozzle design requires a short physicalseparation between the point of admixing and the optical cavity. Whenambient temperature carbon dioxide is admixed with a flowing stream ofnitrogen having a population inversion consisting of vibrationallyexcited molecules, the carbon dioxide undergoes a rapid energy exchangewith the nitrogen, the carbon dioxide being selectively pumped into theupper lasing 001 level. The lifetime for carbon dioxide at this energycondition is very short and unless a short nozzle is used together withvery high velocity gas streams through the nozzle, much of the 001carbon dioxide gas relaxes before this gas is passed from the mixingregion to the optical cavity region where the laser energy can beextracted.

The injection of the carbon dioxide gas should not occur until thestatic temperature (the actual temperature of the gas not consideringthe kinetic energy of the molecule) of the nitrogen is at a level(approximately ambient temperature) that ensures the carbon dioxide willnot be thermally heated to the level. As a practical matter, the statictemperature is about the same as the carbon dioxide gas injectiontemperature. The subject is discussed more fully in Bronfin, B. R.,Boedeker, L. R., and Cheyer, J. R, Thermal Laser Excitation by Mixing ina Highly Convective Flow, Applied Physics Letters, Vol. 16, No. 5, March1, 1970, p. 214.

Although the invention has been shown and described with respect topreferred embodiments thereof, it should be understood by those skilledin the art that the foregoing and various changes and omissions in theform and detail thereof may be made therein without departing from thespirit and the scope of the invention.

Having thus described typical embodiments of our invention, that whichwe claim as new and desire to secure by Letters Patent of the UnitedStates is:

3.. The method of providing laser energy in a gas dynamic mixing laserutilizing nitrogen as an excitation gas and carbon dioxide as a lasinggas, comprising the steps of:

decomposing a liquid hydronitrogen fuel by an exothermic reaction in acatalytic chemical reaction chamber to form a gas mixture includingnitrogen gas molecules which are at thermal equilibrium;

rapidly expanding the gas mixture in an aerodynamic nozzle from a statictemperature not less than about l,200 R to a static temperature ofapproximately 550 R to establish a nonequilibrium condition in thevibrational energy levels of the nitrogen admixing carbon dioxide whichis at a temperature no greater than about 550 R to the expanded gasmixture in the nozzle to form a gas admixture in which energy containedin the vibrational energy levels of the nitrogen is transferred bycollision processes to the carbon dioxide, to establish a populationinversion in the vibrational energy levels of the carbon dioxidemolecules;

passing the gas admixture through an optical chamber stimulatingemission of radiation from said molecules while in said chamber;

exhausting the gas admixture from the optical chamber.

2. The method according to claim 1 further comprising, between the stepof admixing carbon dioxide and the step of passing the gas admixturethrough an optical chamber, the additional step of:

expanding the gas admixture in a nozzle sufficiently to ensure a statictemperature of the gases exiting the nozzle of approximately 550 R.

3. The method according to claim 2 wherein the fuel is selected from thegroup consisting of hydrazine, hydrogen azide, hydrazine azide, ammoniumazide, diimide, triazine, diiminohydrazine, bisdiazoamine,hexazodiazene, heptazodiazene and octazotriene.

41. The method according to claim 2 wherein the fuel is hydrazine.

5. The method according to claim 2 wherein the fuel is selected from thegroup consisting of hydrogen azide and hydrazine azide.

6. The method of providing laser energy in a gas dynamic mixing laserutilizing nitrogen as an excitation gas and carbon dioxide as a lasinggas comprising the steps of:

decomposing a liquid hydronitrogen fuel by an exothermic reaction in acatalytic chemical reaction chamber to form a gas mixture which includesnitrogen gas molecules at thermal equilibrium and an additional gas;

reacting the gas mixture with a reagent to increase the temperature ofthe gases entering the nozzle and to reduce the amount of saidadditional gas present;

rapidly expanding the gas mixture in an aerodynamic nozzle from a statictemperature not less than about l,200 R to a static temperature ofapproximately 550 R to establish a nonequilibrium condition in thevibrational energy levels of the nitrogen gas;

admixing carbon dioxide which is at a temperature no greater than about550 R to the expanded gas mixture in the nozzle to form a gas admixturein which energy contained in the vibrational energy levels of thenitrogen is transferred by collision processes to the carbon dioxide,thereby establishing a population inversion in the vibrational energylevels of the carbon dioxide molecules;

ll! expanding the gas admixture in a nozzle sufiiciently to ensure astatic temperature of the gas exiting the nozzle of approximately 550 R;passing the gas admixture through an optical chamber stimulatingemission of radiation from said molecules while in said chamber;

exhausting the gas admixture from the optical chamber.

7. The method according to claim 6 wherein the additional gas ishydrogen.

8. The method according to claim 7 wherein the hydrogen is chemicallyreacted with a reagent to form water, thereby increasing the temperatureof the gases entering the nozzle and reducing the amount of hydrogenpresent, the amount of hydrogen so reacted being limited so that thewater formed comprises no more than approximately 10 percent by volumeof the gas mixture in the optical chamber.

9. The method according to claim 6 wherein the additional gas isammonia.

10. The method according to claim 9 wherein the ammonia is chemicallyreacted with a reagent to form water and nitrogen, thereby increasingthe temperature of the gases entering the nozzle and reducing the amountof ammonia present, the amount of ammonia so reacted being limited sothat the water formed comprises no more than approximately 10 percent byvolume of the gas mixture in the optical chamber.

zg gy UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,694, 770 Dated September 26, 1972 Inventor(s) Wayne G. Burwell andCharles Oickle, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Claim 1, column 8, line 51 after "chamber;" insert --and-- Claim 6,column 10, line 2 delete "gas" and insert --gases- Claim 6, column 10,line 6 after "chamberg" insert -and-- Signed and sealed this 13th day ofFebruary 1973..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3,694, 770 Dated September 26, 1972 Inventor(s) Wayne G.Burwell and Charles Oickle, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Claim 1, column 8, line 51 after "chamber;" insert --and-- Claim 6,column 10, line 2 delete "gas" and insert --gases-- Claim 6, column 10,line 6 after "chamber;" insert --and-- Signed and sealed this 13th dayof February 1973..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Connnissionerof Patents

2. The method according to claim 1 further comprising, between the stepof admixing carbon dioxide and the step of passing the gas admixturethrough an optical chamber, the additional step of: expanding the gasadmixture in a nozzle sufficiently to ensure a static temperature of thegases exiting the nozzle of approximately 550* R.
 3. The methodaccording to claim 2 wherein the fuel is selected from the groupconsisting of hydrazine, hydrogen azide, hydrazine azide, ammoniumazide, diimide, triazine, diiminohydrazine, bisdiazoamine,hexazodiazene, heptazodiazene and octazotriene.
 4. The method accordingto claim 2 wherein the fuel is hydrazine.
 5. The method according toclaim 2 wherein the fuel is selected from the group consisting ofhydrogen azide and hydrazine azide.
 6. The method of providing laserenergy in a gas dynamic mixing laser utilizing nitrogen as an excitationgas and carbon dioxide as a lasing gas comprising the steps of:decomposing a liquid hydronitrogen fuel by an exothermic reaction in acatalytic chemical reaction chamber to form a gas mixture which includesnitrogen gas molecules at thermal equilibrium and an additional gas;reacting the gas mixture with a reagent to increase the temperature ofthe gases entering the nozzle and to reduce the amount of saidadditional gas present; rapidly expanding the gas mixture in anaerodynamic nozzle from a static temperature not less than about 1,200*R to a static temperature of approximately 550* R to establish anonequilibrium condition in the vibrational energy levels of thenitrogen gas; admixing carbon dioxide which is at a temperature nogreater than about 550* R to the expanded gas mixture in the nozzle toform a gas admixture in which energy contained in the vibrational energylevels of the nitrogen is transferred by collision processes to thecarbon dioxide, thereby establishing a population inversion in thevibrational energy levels of the carbon dioxide molecules; expanding thegas admixture in a nozzle sufficiently to ensure a static temperature ofthe gas exiting the nozzle of approximately 550* R; passing the gasadmixture through an optical chamber stimulating emission of radiationfrom said molecules while in said chamber; exhausting the gas admixturefrom the optical chamber.
 7. The method according to claim 6 wherein theadditional gas is hydrogen.
 8. The method according to claim 7 whereinthe hydrogen is chemically reacted with a reagent to form water, therebyincreasing the temperature of the gases entering the nozzle and reducingthe amount of hydrogen present, the amount of hydrogen so reacted beinglimited so that the water formed comprises no more than approximately 10percent by volume of the gas mixture in the optical chamber.
 9. Themethod according to claim 6 wherein the additional gas is ammonia. 10.The method according to claim 9 wherein the ammonia is chemicallyreacted with a reagent to form water and nitrogen, thereby increasingthe temperature of the gases entering the nozzle and reducing the amountof ammonia present, the amount of ammonia so reacted being limited sothat the water formed comprises no more than approximately 10 percent byvolume of the gas mixture in the optical chamber.